Trader Johann arrives at Berk and the Riders are already expecting his arrival, but Snotlout states that he doesn't let him touch any of his goods because the last time Trader Johann was at Berk Snotlout broke half of his cool stuff. While the Riders are enjoying their time looking around Johann's ship, Gobber finds mass quantities of scrap metal on board and decides to take it to his workshop toothless sniffs some of the goods then he sees a butterfly and starts chasing him until it goes to sit on his nose
Meanwhile toothless tries to resist his sneeze The Riders (except Snotlout) helps Gobber's scrap metal to be delivered to his workshop, meanwhile Toothless is still chasing the butterfly but he sneezes causing the butterfly to fly away
At nightfall, an unknown thick fog travels and explores the village and targets Gobber's scrap metal. At morning, some of the town's metal has been stolen including Tuffnut's mace, who he calls it 'Macy', that he bought from the Trader Johann and goes miserable without it. Hiccup and Astrid starts their investigation by looking at Gobber's workshop, and they find no footprints or clues for the metal thief, even though Gobber has set several booby traps around his workshop, that he accidentally set it on. Next, they investigate at the Twins' house where they find Tuffnut's shrine for 'Macy', but still they find no clues or footprints in the location, but Tuffnut still suspects that Ruffnut stole it. Hiccup and Astrid decide that they continue their investigation tomorrow.
Late at night, the unknown thick fog travels through Berk again, and stealing all the town's metal. As the fog enters through Hiccup and Stoick's house, they steal metal along their way up to Hiccup's room. Toothless wakes up and witness the fog, while Hiccup gets lifted and the fog tries to take his metal leg. Toothless tries to pull Hiccup away from the fog, but gets a tickle in his nose Toothless sneezes the fog away by using his nose and reveals that the metal thief is actually Smothering Smokebreaths. Before they make their exit, they steal some of Hiccup's metal things but unable to grab his helmet and the Smokebreaths escape the room.
At dawn, most of the town's metal is now stolen including the Riders' viking helmets. Hiccup informs them that the theif is actually Smothering Smokebreath dragons, but it is still unclear of how and why the Smokebreaths get to Berk as they are excluded in Breakneck Bog, Gobber interrupts and shouts that the Smokebreaths stole his scrap metal from Trader Johann. Hiccup suddenly suspects Trader Johann.
At the Great Hall, Hiccup and Stoick ask Johann where he got the vast quantities of scrap metal. Johann reveals that he got the scrap metal from a Beserker with a great price, and made the deal in Breakneck Bog. Hiccup tells Johann that the scrap metal he got was from a Smokebreath nest filled with hatchlings, Stoick and Hiccup leaves in anger, including Toothless who interrupts his snack. Stoick and Hiccup watches the villagers struggling to continue their daily lives, as most of their things is now made of wood unable to support most of the weight, even worst Gobber informs that almost all of the town's metal is depleted and the Armory is lacking weaponry making Berk mostly vulnerable for an invasion. Hiccup and the Riders must find the missing metal before an invasion by Dagur is settled, Fishlegs tells that the Smothering Smokebreaths can't be far due to carrying all the metal weight. Hiccup suggests that the Smokebreaths' build a nest at Berk. But they don't have time to find their nest, Hiccup suggests they lure it by gathering all the last drop of metal resources in Berk and let them steal it and follow them to where they would bring it, Snotlout is force to leave his spare metal helmet.
The Smothering smokebreaths have taken the bait, and the Riders wait for the perfect time to jump in but the Twins' quickly execute the plan by attacking the seemingly Smokebreaths still at the area, only later to be revealed they are attacking themselves. The Smokebreaths' cover splits into two, forcing the Riders to split up. Hiccup and Toothless follows one, almost losing it, but manage to find another batch of them. They struggle as the Smokebreaths begin to corner them and wants to take their metal, a Smokebreath steels Toothless' metal rod and making him unable to fly and gently crashes down, they are forced to follow the Smokebreaths on foot. Hiccup and Toothless closes in, and Hiccup uses his shield to catch the Smokebreath that took the rod, but proves stronger than him and drags him along the way on the ground. The Smokebreath gives up the rod and the rope that's pulling him breaks apart. Hiccup and Toothless stumble to the location of the Smokebreaths new nest. Astrid finds Hiccup and informs him that a large scale Beserker and Outcast invasion is sailing toward Berk's territory.
It's revealed that Dagur and Salvage planned to offer the stolen scrap metal filled with hatchlings to Trader Johann, and later make Berk mostly vulnerable. Hiccup comes up with a plan, thanks to Tuffnut, and orders the villagers to give their last spare of metal and gather it, Gobber volunteers to give to Hiccup his arm-weapon that he took his first Outcast with, and tells Hiccup to take good care of it. The Riders lure the Smothering Smokebreaths away from their nest, by using the last metal resource of Berk. Dagur is being impatient that no movement or attack is coming in their way, but finally arrives, they arm their weapons to prepare for the attack. Stoick and the other Vikings make their last stand, while the Riders closes in the fleet so is the thick fog, making Dagur's armada unable to see the Berk mainland and is unable to fire any target. The Riders drop their metal load, and Dagur is wondering why they are dropping spoons, but actually it's their plan, as dozens of Smokebreaths attack their fleet and steal all their metal while in the process. They are unable to attack the Smokebreaths, and within minutes the entire fleet is left without metal support and their ships begins to disassemble, completely. The Beserkers are force to retreat, and while Dagur brags that it's not over two Smothering Smokebreaths steal his kneecap and helmet. Toothless finds a butterfly and starts chasing it and the butterfly then goes to sit on his nose
Hours later, The Riders are able to return most of the town's metal including Tuffnut's mace who is finally glad to see it. Stoick ask Hiccup of how he plans to drive away the Smokebreaths from Berk. Hiccup plans to put the scrap metal bait on Trader Johann's ship in attempt to drive away the Smokebreaths, Johann heads for Breakneck Bog and struggles to keep the Smokebreaths out of his ship's deck. While Hiccup and Toothless watches on and escorts him to get to the island. The episode ends with toothless having a butterfly on his nose and he sneezes
- Jay Baruchel as Hiccup
- America Ferrera as Astrid Hofferson
- Christopher Mintz-Plasse as Fishlegs Ingerman
- T.J. Miller as Tuffnut
- Brook Chalmers as Captain Vorg/Sven
- Chris Edgerly as Gobber the Belch
- David Faustino as Dagur the Deranged
- Michael Goldstrom as Trader Johann
- Nolan North as Stoick the Vast
- Zack Pearlman as Snotlout Jorgenson
- Paul Rugg as Savage
- Andree Vermeulen as Ruffnut
- Toothless - Night Fury (Hiccup's Dragon)
- Stormfly - Deadly Nadder (Astrid's Dragon)
- Meatlug - Gronckle (Fishlegs's Dragon)
- Hookfang - Monstrous Nightmare (Snotlout's Dragon)
- Barf and Belch - Hideous Zippleback (Ruffnut and Tuffnut's Dragon)
- Smothering Smokebreath
- This is the second episode in the series where a Smothering Smokebreath attempted to steal Hiccup's metal leg.
- This is also the second episode in the series where we see Astrid without her metal shoulder pads and Fishlegs, Ruffnut, and Tuffnut without their helmets.
- This is the first episode where we see Snotlout and Dagur without their helmets.